Their IMAP implementation is anything but compliant or functional. They implement labels as folders. Every time you use a label, it downloads that message multiple times and puts it into folders.
Also when you try to write drafts in Thunderbird for Gmail, it stores them in such a way as each saved draft turns into part of the conversation (WTF?!) It makes conversations totally unreadable.
I quite gmail years ago and do not miss their broken IMAP implementation.
Fair enough, I guess it's about differing usecases. The few labels that I do use on gmail are set up such that they are indistinguishable from folders (if they match a filter, they don't go in my inbox, and I don't have any overlapping labels). I also rarely have lingering draft emails, so I guess I've not noticed that particular issue (though I do use Mail.app, not thunderbird). Gmail's imap support has been adequate for me since they introduced it however long ago that was. YMMV
Edit: my point about standards compliance for gmail imap was purely about it actually working with third party clients, I've always known that it doesn't conceptually work the same way as a standard imap server.
Also when you try to write drafts in Thunderbird for Gmail, it stores them in such a way as each saved draft turns into part of the conversation (WTF?!) It makes conversations totally unreadable.
I quite gmail years ago and do not miss their broken IMAP implementation.